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AFE4300 IMPEDANCE SYSTEM GAIN, CURRENT CONTROL, ADC SPS

Mastro
Prodigy 110 points
Hello,
I am using an MSP430F2234 uC. I am trying to measure my on board 100R and 1k reference resistor and a third resistor.
The RDY signal is always constant and at VDD. I am performing both one shot and continuous measurements and I see no change at RDY.
Is there a way to set the gain of the recording amplifier for the impedance measurements?
By connecting a resistor in series with the capacitor between pin 19 and 20, the resistor allows the control of the injected current, correct? What is the smallest current we can inject in the way?
What does ADC SPS change? How should one choose the setting for the ADC conversion rate? The signal being converted is DC, right?
Thank you.
  • 0
    TI__Mastermind 18285 points

    Mastro,


    We have received your post and hope to have a response back to you soon.

  • 0 in reply to Amy Schnoor
    Prodigy 110 points
    Dear Amy,

    I was wondering if you could get back to me please.

    RDY is always at VDD.

    My settings are

    writeRegister(MISC1_REGISTER,0x8000);
    writeRegister(MISC2_REGISTER,0x7FFF);
    writeRegister(MISC3_REGISTER,0x0030);
    writeRegister(ADC_CONTROL_REGISTER,0x4100);
    writeRegister(ADC_CONTROL_REGISTER_2,0x0011);
    writeRegister(DEVICE_CONTROL_1,0x6006);
    writeRegister(DEVICE_CONTROL_2,0x0000);
    writeRegister(ISW_MATRIX,0x0000);
    writeRegister(VSW_MATRIX,0x0000);
    writeRegister(ADC_CONTROL_REGISTER_2,0x0063);
    writeRegister(BCM_DAC_FREQ,0x000F);
    writeRegister(IQ_MODE_ENABLE,0x0000);
    writeRegister(WEIGHT_SCALE_CONTROL,0x0000);


    Could you please tell me how long it takes for the RDY to go high once a measurement is ready? (tconv from the data sheet Figure 12)
    What is the fastest frequency to read out the output register? It looks like the data is never ready in my system and I'm reading the content of the output register randomly. Can the output register be read while the conversion is in progress, would it affect the readout routine?

    Please let me know,

    Kind regards,

    Mastro.
  • 0 in reply to Mastro
    TI__Mastermind 49186 points
    Hello Mastro,

    To enable the RDY pin function as a conversion ready signal, the following registers must be modified after reset.

    MISC_REGISTER1 (reg addr: 02h) must be programmed to 0000h
    MISC_REGISTER2 (reg addr: 03h) must be programmed to FFFFh
    ADC_CONTROL_REGISTER1 (reg addr: 01h; bits[3:0]) must be programmed to 0h

    To answer your other questions:
    1. the gain of the amplifier in BCM signal chain is non-programmable.
    2. Yes the resistor in series can control the injected current. The injected current to the human body is limited and it is under the demands of the IEC- 60601 spec. The device follows the IEC restrictions for the injected current. Could you provide more details about your application? Why do you require lower currents? Are you concerned about patient safety etc?
    3. The ADC SPS change the output data rate. While lower data rates improves the ADC input referred noise, it increases the time per sample which is dependent on the application.